Aromatic polyepoxide resins, particularly those based upon the use of polyglycidyl ethers of bisphenol A, have widely been used in applications requiring resistance to high temperature and resistance to chemicals. They have been widely used for preparing electrical laminates for circuit board applications and composites.
Heat cured epoxy resins incorporating a heat activated curing agent have been widely used in applications requiring high resistance to chemicals such as electrical lamination and sealants. One of the problems with epoxy resins is their brittleness and attempts have been made to modify these resins through the addition of toughening agents. Toughening agents are based upon the incorporation of aliphatic diepoxides and ester type plasticizers. More recent technology describes incorporation of urethane polymers and carboxy terminated polybutadiene/acrylonitrile copolymers and epoxy adducts of such copolymers.
Representative patents and literature which describe polyepoxide resins and the approach to enhancing the physical properties of the polyepoxide resins through incorporation of urethanes, rubber, etc., are as follows:
U.S. Pat. No. 3,876,618 discloses oxazolidinone modified triglycidyl ethers of trihydroxy triphenyl methane and their derivatives cured with polyamines to form thermoset resins having outstanding physical properties, adhesion to metals, etc., with utility in the encapsulation of electrical components, laminates for electronic printed circuit boards at elevated temperatures, etc. In producing the oxazolidinone modified triglycidyl ethers, a triglycidyl ether of trihydroxy triphenyl methane is reacted with a polyisocyanate such as toluenediisocyanate, methylene di(phenylisocyanate) and isophoronediisocyanate under conditions such that the isocyanate and epoxy react to form the oxazolidinone structure.
U.S Pat. No. 3,737,406 discloses a process for preparing polyoxazolidones, wherein a polyepoxide is reacted with a polyisocyanate in the presence of chemically reactive epoxy-onium catalyst. The products have a wide range of application such as electrical potting, encapsulant, caulking and adhesive as well as concrete cementing agent.
U.S. Pat. No. 4,163,096 discloses epoxy resins having enhanced toughness imparted thereto wherein the epoxy resins are hardened with liquid polymers containing reactive end groups; e.g., butadiene-acrylonitrile polymers having carboxyl end groups. High viscosity is the problem associated with this product. To alleviate high viscosity, a portion of the glycidyl ether of the polyphenol is reacted with a monoisocyanate, e.g., an aromatic, an aliphatic, cycloaliphatic or aliphatic isocyanate.
U.S. Pat. No. 4,742,146 discloses the use of urethane oligomer modified epoxy resins formed by the copolymerization of an epoxy resin and a urethane oligomer containing an oxyalkylene group and polymerizable ethylenically unsaturation in the presence of a catalyst sufficient for effecting oxazolidone formation. The modified epoxy resin compositions can be cured with conventional curing agents and to prepare urethane modified vinyl ester resins.
U.S. Pat. No. 4,424,316 discloses products formed by the reaction of a diepoxide with mono- and preferably dicarboxylic acids followed by reaction with a polyisocyanate to form a poly(oxazolidone/urethane) thermoset composition. The thermoset compositions are suited for fabrication of molded articles and can be combined with conventional reinforcing agents, e.g., glass fiber, aromatic polyamide fiber, etc.
U.S. Pat. No. 4,562,227 discloses the production of heat hardenable reaction resin mixtures containing polyfunctional epoxides and polyfunctional isocyanates. One component of the resin reaction mixture is an isocyanate prepolymer formed by reacting a polyisocyanate with a diol where the isocyanate is reacted in a proportion of 0.01 to 0.35 equivalence per diol, and the resulting isocyanate prepolymerizate in a polymethylene polyphenyl isocyanate and an epoxy resin is reacted. Oxazolidone and isocyanate (OX/ICR) formation is effected through the use of an accelerator.
U.S. Pat. No. 5,112,932 discloses epoxy terminated polyoxazolidones formed by reacting a polyisocyanate with an epoxide. A combination of oxazolidone rings and isocyanurate rings can be achieved.
U.S. Pat. No. 4,719,267 discloses heat curable, one package epoxy resins incorporating polyurethane prepolymers having amine blocked isocyanate groups. Blocked amine curing agents are incorporated into the resin to form sealants.